Method of carburizing iron articles



Patented Mar; 5, 1935 I UNITED .,1,992 ,9s1 I METHOD or cannomzmo moN ARTICLES Carl Albrecht, Oronberg, in Taunus, Germany,

assignor to Deutsche Gold & Silber Scheideanstalt vormals Roessler, Frankforton-the-Main,

, Germany, a corporation No Drawing. Application November 21, 1933,

Serial No. 698,989. In Germany November 26,

14 Claims. (01. 148 -15) This invention isconcerned with the cementation and hardening of objects made from iron,

iron alloys, refined steel or special alloy steel and the like. By using theterm iron articles hereinafter and in the appended claims I refer to articles and objects of the above mentioned nature. k

It is already known that the cementation of such iron articles canbe carried out in a fused bath which contains non-cementing salts such as alkali metal chlorides and the like which become liquid at the temperature used for the carburization operation and which contains as carburizing material finely divided carbon. It

is, furthermore, known that the carburizing action of the bath can be considerably improved by adding alkali substances such as for instance alkali metal hydroxides, sodium oxide or the like.

According to my invention the cementation is carried'out in a fused bath which contains as carburizing' material a carbide of the alkaline earth metals such as barium carbide, calcium carbide or the like. The melt to which these carbides are added aremade up essentially by noncementing salts such as common salt, potassium chloride or mixtures of these halogen compounds. In addition, the bath contains according to my invention means of an alkaline nature such as alkali metal carbonates, for example soda carbonate, hydroxides such as sodium hydroxide or oxides such as sodium oxide or mixtures of two or more of these substances. The quantity of the carbides to be added can vary in relatively wide limits and maybe, for instance, between 2 and.15 percent. In some cases the amount may be even greater or, also, smaller than those indicated. Advantageously I add 5 to percent of the alkaline metal carbide to the mixture. The quantity'of the-substance of an alkaline nature such .assoda carbonate, soda hydroxide or the like, may also vary within wide limits. I have found, for instance, that in some cases excellent results were obtained by employing only a few percent such as-2 to 5 percent of sodium hydroxide whilst in other cases the presence of much larger quantities for instance percent and more did not show any deleterious effects. When using carbonate such as sodium carbonate in quantities of up to .50 percent and more I was able to get very good results indeed.

It has'been known that carbides of the alkaline earths, such as calcium carbide or barium carbide could be used for case hardening in a solid pulverulent form, but their use has not been without risk since when the objects after the cementing operation were removed from the pulverulent case hardening mixture and entered into aqueous solutions in order to quench the articles explosions frequently occur-ed. For this reason it was surprising that carbides could be used as cementation means in, fused melts" of inert salts such as common salt, alkaline metal chlorides and the like in presence of an alkaline nature and furnish excellent cementation effects without incurring the 'risk of explosions on quenching the treated objects as they might occur when the carbides are used in the form of a powder. The use of alkaline earth carbides has in comparison with finely divided carbon the great advantage that they are distributed uniformly throughout the whole melt and do not give rise to the formation of scum or dross or, of a solid deposit which settles down at the bottom of the crucible or vessel employed for the melting of the mixture and thus hindering the heat transmission. This is to a certain extent due to the fact that according to my invention small quantities only of alkaline earth carbides are required and are sufilcient to furnish excellent cementation effects.

The components of the. melt as regards their nature and the quantities used are chosen with a view of obtaining as liquid a meltas possible at the temperatures used for the cementation.

Hereby the loss of bath material-is minimized when the articles are lifted from the melt after they have been carburized.

Amongst the cementing substances calcium carbide is the cheapest, and most. easily available in the industry. Barium carbide, on the other hand, gives very excellent results in consequence of the formation in the melt of barium oxide which acts as an alkaline substance and assists suitable for my work range between about 750 V and 1050 centlgrade.

When the bath comes less active I add further quantities of carbide. The addition is carried out advantageously in mixture with further quantities of the other melt components. I prefer to previously melt the carbides with the components to be added and introduce this fused mixture into the melt. I

The cementation layers which I am able to obtain by carrying out the cementation according to my invention are of great depths. For instance I was able to attain layers of 2.4 millimeters by leaving the articles to be cemented in the melt for 6 hours at 930 centigrade. Moreover the cementation layer when working according to my invention with barium carbide, for instance, was free from over-carburization which is also a very great advantage. Furthermore the transition from the carburized layer to the uncarburized core is very gradual so that a cracking oil of the carburized layer does not occur. The hardening effects after quenching are very high ones.

Example 1 Bolts with a carbon content of .1 percent are immersed into a bath containing 10 kilograms potassium chloride, 10 kilograms soda carbonate and 1.1 kilograms calcium carbide. The cementation is carried out at 930 centigrade. After 2 hours the carburizing depth is 1.1 millimeters, after 4 hours 1.4 millimeters.

Example 2 kilograms barium carbide furnished at a tem-' perature of 930 centigrade after 2 hours a cementation depth of 1.1 millimeters, of these .7 millimeter was eutectic. After 4 hours a cementation depth of 1.6 millimeters was obtained, .8 millimeter of which was eutectic. After a further 2 hours, i. e. after a total of 6 hours a penetration depth of 2.4 millimeters was obtained, 1.2 millimeters of which were eutectic- The hardness after quenching was 66 Rockwell.

What I claim is:

1. A method of carburizing iron articles by im mersing said articles in a molten bath which consists of alkaline metal chlorides to which alkaline earth carbides and substances selected from the group consisting of alkali metal carbonates, hydroxides, and oxides have been added.

2. A method of carburizing iron articles by immersing said articles in a molten bath which consists of sodium chloride to which alkaline earth carbides and substances selected from the group consisting of alkali metal carbonates, hydroxides, and oxides have been added.

3. A method of carburizing iron articles by immersing said articles in a molten bath which consists of a mixture of sodium chloride and sisting of alkali metal carbonates, hydroxides, and oxides have been added.

4. A method of carburizing iron articles by' immersing said articles in a molten bath which consists of alkaline metal chlorides to which calcium carbide and a substance selected from the group consisting of alkali metal carbonates, hydroxides, and oxides has been added.

5. A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which barium carbide and substances selected from the group consisting of alkali metal carbonates, hydroxides, and oxides have been added.

6. A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which alkaline earth carbides and sodacarbonate have been added. g

7. A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which alkaline earth carbides and sodium hydroxide have been added.

8. A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which alkaline earth carbides and substances selected from the group consisting of alkali metal carbonates, hydroxides, and oxides have been added, at temperatures of from 750 to 1050 centigrade.

9. -A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which 5 to 10 percent of alkaline earth carbide and asubstance selected from the group consisting of alkali metal carbonates, hydroxides, and oxides has been added.

10. A method of carburizing iron articles by immersing said articles in a molten bath which consists of alkaline metal chlorides to which alkaline earth carbide and from 2 to 10 percent of alkali metal hydroxide have been added.

11. Carburizing bath for cementing iron articles consisting essentially of to parts of alkali metal chlorides, 5 to 15 parts of alkaline earth metal carbide and 2 to 5 parts of alkaline metal hydroxide.

12. Carburizing bath for cementing iron articles consisting essentially of 40 to 50 parts of alkali metal chlorides, 20 to 50 parts of alkali metal carbonate and 5 to 15 parts of alkaline earth carbide.

13. A fused bath for carburizing ferrous articles consisting of an alkaline metal chloride, an alkaline earth carbide, and a substance selected from the group consisting of alkali metal carbonates, hydroxides, and oxides.

14. A mixture for carburizing ferrous articles which consists of an alkaline metal chloride, an alkaline earth carbide, and a substance selected from the group consisting of alkali metal carbonates, hydroxides, and oxides.

CARL ALBRECHT. 

